1. Field of the Invention
The present invention relates to an imaging apparatus to be mounted on a scope end section of an electronic endoscope.
2. Description of the Background Art
Conventionally, an imaging apparatus for an electronic endoscope has a configuration shown in FIG. 1. In this conventional imaging apparatus of FIG. 1, a CCD (charge coupled device) 102 is fixed on one side of a chip carrier 101 made from a ceramic substrate, where pads 103 provided on the CCD 102 and pads 104 provided on the chip carrier 101 are connected by bonding wires 105. Then, a cover glass 106 containing an optical filter is attached on an imaging surface of the CCD 102 by means of an adhesive resin 111 placed therebetween, while the other side of the chip carrier 101 is attached to a flexible print substrate 107 such that they are electrically connected. In addition, the above described structure formed by the chip carrier 101, the CCD 102, the bonding wires 105, the cover glass 106, and the flexible print substrate 107 are covered by a mold resin 108, while the bonding wires 105 are protected by metallic frames 109 attached on the mold resin 108 over the locations of the bonding wires 105. Moreover, on a part of the flexible print substrate 107 not covered by the mold resin 108, chip components 110 are provided. With this configuration, the imaging apparatus is mounted on a scope end section of an electronic endoscope.
However, such a conventional imaging apparatus for an electronic endoscope has been associated with the following problems.
First, a conventional imaging apparatus with a configuration shown in FIG. 1 involves a number of piled up layers such as those for a height of the bonding wires 105, a distance between the bonding wires 105 and the metallic frames 109, a thickness of the chip carrier 101, a thickness of the metallic frames 109, a thickness of the flexible print substrate 107, and a thickness of the mold resin 108, so that a further thinning of a thickness of such an imaging apparatus has been practically impossible, and this in turn obstructed the further thinning of the scope end section of the electronic endoscope.
Secondly, the cover glass 106 is attached on the imaging surface of the CCD 102 by means of the adhesive resin 111 placed therebetween, such that micro-lenses (not shown) provided on the imaging surface of the CCD 102 are buried inside the adhesive resin 111. Here, because the index of refraction of the adhesive resin 111 is very close to that of the micro-lenses so that the light beam will hardly be refracted at a boundary between the adhesive resin 111 and the micro-lenses. As a consequence, an effect of improving a sensitivity of the CCD 102 due to the presence of the micro-lenses cannot be obtained.
Thirdly, the cover glass 106 cannot be made larger because of the possible interference between the cover glass 106 and the pads 103 of the CCD 102. As a result, it has been impossible to keep the reflections by the side surfaces of the cover glass 106 out of the imaging surface of the CCD 102.
Finally, in the imaging apparatus for an electronic endoscope, it is necessary to arrange the imaging surface of the CCD 102 to be perpendicular with respect to a light beam axis of an incident light beam. However, in the conventional imaging apparatus for an electronic endoscope, the cover glass 106 is attached on the imaging surface of the CCD 102 by means of the adhesive resin 111 placed therebetween as already mentioned above, so that it is difficult for the imaging surface of the CCD 102 to be arranged accurately in a desired direction because it is difficult to accurately control the thickness of the adhesive resin 111 during its hardening process.